(1) Field of the Invention
The present invention relates generally to a permanent locating system that may be used to selectively access wellbore sections and/or for other purposes. In a more particular embodiment, the present invention is especially suitable to provide reliable and repeatable downhole whipstock orientation.
(2) Description of the Prior Art
It is often desirable, in both cased and open hole, to branch off one or more times from an existing wellbore or to sidetrack away from an object such as a fish or toward an object such as a revised geological target. A whipstock may be used as a guide for the drill bit or mill in creating the new borehole sections, casing windows, and the like, so that the new borehole section is oriented in the desired direction. The whipstock is anchored in the wellbore at the desired depth at which the new well is to be kicked off. The bit or mill engages the generally metallic whipstock face or surface that is typically angled so as to urge the bit or mill in a desired direction. In this manner, it is well known that the mill or drill bit is thereby directed to mill or drill in the direction intended for the new wellbore section. The whipstock face may be left in the existing wellbore to guide the drill string, production string, and the like into the new borehole section.
However, at some time after the new wellbore branch is drilled, it may be desirable to obtain access to the original borehole such as with a drill string or production string. Moreover after gaining access to the original borehole once again, sometime later it may be desirable to reliably obtain access once again to the new wellbore branch with a drill string and/or production string. Moreover, there may be multiple branches in the wellbore and it may be desirable to be able to reliably and selectively obtain access to any one of them. In the past, bent drill strings and subs have been used for this purpose, but often with little success. Generally, obtaining access to the various sections of the wellbore has been unreliable at best.
Consequently, it would be desirable to provide a system and method that is designed to reliably and consistently control access to any branch or borehole section as desired. Those skilled in the art will appreciate the present invention that addresses the above and other needs and problems.
Accordingly, it is an object of the present invention to provide an improved location system and method. It is yet another object of the present invention to provide an improved system and method for reliably obtaining access to any wellbore branch or section.
It is yet another object of the present invention to provide a permanent downhole depth and orientation reference which does not prevent re-entry into the mother wellbore. These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.
Therefore, in accordance with the present invention, a method is disclosed for providing a reference in a borehole to a selectable depth and selectable orientation, comprising one or more steps such as positioning a reference sleeve within the borehole, expanding the reference sleeve radially outwardly within the borehole at the selectable depth and with the selectable angular orientation such that the reference member fixably engages the borehole so as to be mounted in the borehole. Preferably the reference sleeve internal diameter increases as the reference sleeve expands radially outwardly so as to permit larger diameter elements to extend there through if needed.
Other steps may include providing a whipstock assembly to be removably engagable with the reference sleeve, and/or providing the whipstock assembly with mating surfaces to the reference sleeve such that when the whipstock assembly is engaged with the reference sleeve, then the whipstock assembly is positioned at the selectable depth and the selectable orientation.
In a preferred embodiment, the method may include one or more steps such as forming a new borehole section, removing the whipstock assembly, and leaving the reference sleeve within the borehole.
If it is desired to return to the original borehole, the method may include extending a pipe string past the new borehole section and through the reference sleeve. If it is then desired to return to the new borehole section, then the method may include steps such as mounting the same or equivalent whipstock assembly in the reference sleeve, and extending a pipe string into the new borehole section.
In a presently preferred embodiment the method includes the step of providing that the reference sleeve has sufficient length and hence sufficient contact area to securely affix the reference sleeve in the borehole as a result of the step of expanding.
To expand as desired, the method may provide that the reference sleeve is formed as a tubular spring. The method may then comprise compressing the reference sleeve radially inwardly in a running position, and securing the reference sleeve in the running position. At the desired borehole position, the method may further comprise releasing the reference sleeve from the running position such that the reference sleeve springs radially outwardly.
In one embodiment, the method may further comprise providing one or more reference slots in the reference sleeve for the selectable orientation, and providing one or more keys on the whipstock assembly for engaging the one or more slots for positioning the whipstock assembly at the selectable orientation. In this case, the method may also comprise guiding the one or more keys into the one or more slots with one or more guide surfaces.
Thus, an assembly is provided for selectively entering a first borehole section or a second borehole section which may comprise one or more elements such a tubular reference sleeve which is moveable between a radially closed running position and a radially open anchoring position. Preferably, the tubular reference has a smaller outer diameter in the running position so as to be movable within the first borehole. The tubular reference sleeve engages a wall of the first borehole section in the anchoring position. One or more orientation surfaces may be provided on the tubular reference sleeve such that the one or more orientation surfaces are moveable radially outwardly in the open anchoring position.
In a preferred embodiment, the tubular reference sleeve forms a spring which is expanded in the radially open position.
The assembly may further comprise a whipstock assembly having one or more mating surfaces for engaging the one or more orientation surfaces on the tubular reference sleeve. The whipstock assembly may be removably mountable to the reference sleeve. Preferably, the reference sleeve is engagable with the borehole along a length sufficient for affixing the reference sleeve within the borehole in the anchoring position. In other words, a method may be provided for selectively entering one of a plurality of borehole sections comprising one or more steps such as radially expanding a reference sleeve to affix the reference sleeve in a first borehole section, and providing a whipstock engagable with the reference sleeve to permit entry into a second borehole section.
Additional steps may include removing the whipstock from the reference sleeve to provide for entry into the first borehole section and/or subsequently replacing the whipstock within the reference sleeve to provide for entry into the second borehole section. Other steps may preferably include providing the reference sleeve and the whipstock with mating engagement surfaces such that the whipstock is oriented when the whipstock engages the reference sleeve.